For a 55 gallon you have a lot of options, especially with a T5. You could have amazon swords, ludwigia, water wisteria, rotala, hygrophilas, dwarf sag, crypts, Anubias, java fern, any moss pretty much, and much more.

I would use Flourish root tabs, follow the directions for putting them in the substrate so you have nutrients at the roots and then Seachem Flourish Comprehensive Supplement. Make sure it isn't another product on the Flourish line.